Why did Jesus explain the parables to the disciples only and not to the crowd?

He did have some parables for the crowd too. We read at Mathew 5:1,2, "When he saw the crowds, he went up on the mountain; and after he sat down, his disciples came to him. 2 Then he opened his mouth and began teaching them..."

We read at Matthew 6:25-31. Verse 25 &26: "On this account I say to you: Stop being anxious about your lives as to what you will eat or what you will drink, or about your bodies as to what you will wear. Does not life mean more than food and the body than clothing? 26 Observe intently the birds of heaven; they do not sow seed or reap or gather into storehouses, yet your heavenly Father feeds them. Are you not worth more than they are?" This whole chapter talks about Jesus' sermon on the Mount. Then at Matthew 7:28,29 we read, "When Jesus finished these sayings, the effect was that the crowds were astounded at his way of teaching,  for he was teaching them as a person having authority, and not as their scribes."

(New World Translation of the Holy Scriptures)